The basic idea of positioning a roller type of window screen vertically in a window frame to change its effective area of screening is old in the art. Various devices have been patented and those known to the applicant at the time which are considered to be the closest prior art are summarized briefly below.
Thiel, U.S. Pat. No. 394,737 utilizes an ordinary roll-up type of window shade and instead of mounting it at the top of the window opening provides for its riding on guide rods at the sides of the window with a pulley and rope arrangement to raise and lower the screen roller to any desired position.
Brown, U.S. Pat. No. 938,207 teaches the use of angle iron brackets at the sides of the window providing rails from which L-shaped plates are permitted to ride, said plates holding the roller in position which may be altered by the use of suitable rope and pulley arrangements mounted on the window frame and attached to the sliding slide plates holding the roller.
Joseph, U.S. Pat. No. 1,303,678 teaches the use of horizontal metal slats to hold the screen roller which are positioned vertically in the window screen by means of chain and sprocket combinations, provisions being made to hold the chain in a given and consequently provide for changing the location of the roller.
Heck, U.S. Pat. No. 4,202,395 utilizes vertically movable bars with zig-zag panels in between, the bars being changeable in location by means of parallel cords which in turn cause the bars to act on the slats after the manner somewhat of a venetian blind. The cord arrangement is of parallelogram configuration and is very different from the arrangement of applicant.
Hopkins, U.S. Pat. No. 785,806 uses a hollow roller through which cords pass connecting with sliding crossheads moving in vertical grooves which hold the roller and hence the shade in a proper horizontal position.
My U.S. Pat. No. 4,326,577 utilizes hollow rollers and tension cords so arranged in or upon a window frame as to remain in tension at all times and hold the rollers in any given desired position because of their novel method of threading through the rollers and attaching to the frame. In that invention I use two sets of cords of two each or a total of four which somewhat complicates the tension adjustment of the cords.